In conventional membrane IR sensors, little to no attention has been paid toward transmissivity of IR near metal traces. Because of the arrangement of these membrane sensors, reflection of IR was generally not a factor. However, when the sensor absorber is behind the metal traces (for example, a Wafer Level Chip Scale Package or WCSP package) the metal traces can substantially block or reflect the IR radiation away from the absorber and can affect the operation and reliability of the IR sensor. Therefore, there is a need to increase the transmissivity of a membrane IR sensor that uses the substrate as a visible light filter.
An example of a conventional system is PCT Publ. No. WO2010029488.